Detecting the presence of an entity in a specific area is a need which arises in many different situations. Applications which make use of such a detection include intrusion in a security perimeter or detection of an entity in an area having systems, or actuators, that can be dangerous for this entity.
Several detection systems have been developed and installed for sensing an entity in a specific area or for detecting an entity in a area that includes some risk for that entity. Some systems use motion sensors and assess changes in ambient temperature produced by a moving entity. They are therefore not designed to detect a moving entity since its temperature is typically the same as the ambient temperature. Also, motion sensors are not capable of detecting a stationary entity. Another alternative is to use an infrared source and an infrared receiver to detect the presence of an entity. Detection occurs when an entity interferes with the reception by the receiver of the emitted infrared signal. Even if several sources and receivers are installed to cover the surface of the monitored area, gaps always exist, leaving areas not covered by the entity detection system. Thus, there is a need for improvements in the detection of entities in monitored areas.
An example of where this need is felt is in the area of mobile storage systems. The optimization of space for storing different kinds of material is the main benefit of mobile storage systems. However, using a mobile storage system implies security issues. When the need to open an aisle explicitly requires to close another aisle, it is very important to detect the presence of an entity in the aisle before closing it. Thus, there is a need for improvements in the detection of moving and stationary entities in mobile storage systems.